1. Field of the Invention
The present invention relates to a webbing retractor employed in a seatbelt system for a vehicle designed to restrain the body of an occupant in an emergency situation of the vehicle, the webbing retractor being adapted to instantaneously stop the webbing of the seatbelt system from being unwound when an emergency situation of the vehicle occurs.
2. Description of the Related Art
In a typical seatbelt system, one end of an occupant restraining webbing is wound up in layers on a take-up shaft of a webbing retractor.
One type of such take-up shaft has heretofore been arranged such that, when the vehicle is in a normal state, the take-up shaft is allowed to rotate in a direction in which the webbing is unwound, whereas, when the vehicle runs into an emergency situation, an acceleration sensor detects it and causes a lock bar to engage with a main gear wheel rotating together with the take-up shaft, thereby locking the take-up shaft from rotating in the webbing unwinding direction, and thus enabling the occupant's body to be restrained by the webbing.
The lock bar is actuated to engage with the main gear wheel through a friction spring in response to the rotation of an inner gear wheel which is rotatably supported by the take-up shaft.
The rotation of the take-up shaft is applied to the inner gear wheel through a pawl which is adapted such that, when the vehicle is in a normal state, the pawl is separated from the inner periphery of the inner gear wheel and rotates around the take-up shaft, whereas, when the rotation of the pawl is delayed with respect to the rotation of the take-up shaft, one end portion of the pawl is meshed with the inner gear wheel.
The delay in rotation of the pawl is caused by the acceleration sensor, and a lock wheel is interposed between the acceleration sensor and the pawl.
The lock wheel is rotatably supported by the take-up shaft, and a pin which is provided at a part in the radial direction thereof is pivotally supported by the pawl, whereby the rotation of the take-up shaft is transmitted to the lock wheel through the pawl.
Accordingly, when the lock wheel is stopped from rotating by the action of the acceleration sensor, the rotation of the pawl is delayed with respect to the rotation of the take-up shaft, and the pawl is thereby meshed with the inner gear wheel.
In this type of the conventional webbing retractor, the lock bar may be so firmly meshed with the main gear wheel that they fail to disengage from each other even after an emergency situation has ceased.
In order to forcedly disengage them, a spool release mechanism is installed in the above-described retractor, and the lock bar can be disengaged from the main gear wheel by actuating this mechanism.
However, when the lock bar and the main gear wheel are disengaged from each other to allow the webbing to be unwound from the take-up shaft, there are cases where the acceleration sensor and the lock wheel remain engaged with each other, and if the webbing is forced to be unwound in this state, the constituent elements of the acceleration sensor and the lock wheel may be damaged.